Over the years, many of the traditional sources for fish, i.e. lakes, rivers, streams, etc., have become contaminated with pollutants generated by the public. As a result, fewer fish are available in such sources; and, in addition, fish that are able to survive in the contaminated waters often themselves become contaminated and unfit for human consumption.
The reduced supply of consumable fish from natural sources has resulted in substantial interest and growth of aquaculture systems, in which fish suitable for human consumption are raised in a contaminate-free, non-natural environment.
Aquaculture systems typically include a container containing a large quantity of water in which the fish are raised, and a filtration system for cleaning the water in the container. Such filtration systems typically include a particulate filter and a bio-filter. The particulate filter is used to remove solid particulate materials, such as fish waste and uneaten food, from the water. The bio-filter contains bacteria which removes ammonia and nitrates from the water, and also is used to oxygenate the water.
Various types of filters have been used as particulate filters in aquaculture, including rotating drum filters. The use of rotating drum filters in aquaculture, however, has been limited by their high cost, their need for frequent maintenance, and the difficulty in cleaning the filtering surface of the filtering media. The filtering surface must be continuously cleaned to prevent the filtering surface from being clogged by the particulate matter. Early rotating drum filter systems used high pressure water jets to clean the filtering surface. Such, cleaning methods, however, required the consumption of a large volume of water which had to be disposed of in an environmentally safe manner. More recent drum filter systems use vacuum cleaning devices for removing the particulate from the rotating drum on a continuous basis.
One known prior art rotating drum filter includes a rotating drum positioned in a filter container with an axis of the drum orientated diagonally with respect to the surface of the water in the container. Water flows into the container and travels through the filtering screen of the drum and out an outlet in the container. As the drum filter is rotated, a vacuum positioned in close proximity to the filter screen removes particulates lying on top of the surface of the screen and transports them by air to a separator tank where the particulate matter is separated from the main vacuum air flow.
Such known prior art system includes a 100 mesh nylon filter screen attached to the rotating drum for receiving the flow of water to be filtered. To prevent wear of the filter screen, a polypropylene screen 0.045 inches thick is interposed between the filter screen and the vacuum head. Thus, the vacuum head does not ride directly on the filter screen. Such a system has a water filtration capacity of about 200 gallons per minute.
By positioning the filter diagonally in the container, the width of the filter's surface is restricted to less than half of the overall width of the filter container. Furthermore, since the prior art system places a plastic screen over the filtering material, the vacuum head does not come in contact with the filter surface, and thus, requires a vacuum which generates sufficient suction to remove particles from the filter surface without contacting the filter surface.